1. Field of the Invention
The present invention relates to a solid-state image sensor having a good light collection efficiency, and a method for producing the same.
2. Description of the related Art
Recently, the main body of a digital camera spreading rapidly has a solid-state image sensor for converting a subject light to be picked up into a light signal for recording, such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) sensor assembled. Such a solid-state image sensor in general comprises a light receiving eminent for receiving a subject light to be picked up and converting-the same into a photoelectric signal, a color filter formed on the light receiving element, and a micro lens for improving the light collecting rate to the light receiving element.
In general, the CMOS sensor comprises a signal readout circuit such as a signal amplifier transistor, corresponding to each light receiving element (photo diode) for receiving a light beam to convert the same into a light signal. However, recently, for the purpose of restraining the signal noise or achieving the high integration, a CMOS sensor comprising a signal readout circuit provided commonly for a plurality of light receiving elements called a plural pixel sharing structure is proposed (see Japanese Patent Application Laid-Open (JP-A) No. 1988-100879).
According to a solid-state image sensor comprising such a plural pixel sharing structure, a certain limitation may be generated in terms of the arrangement of a gate electrode and a wiring for achieving such as a high integration. From the configuration structure, the central position of a micro lens (or a pixel area) and the central position of a light receiving element may not coincide in the plan view in some cases. Furthermore, since the displacement degree differs depending on each pixel area, a problem may be generated in that the same light collection cannot be obtained among the pixels for an oblique light beam, or the like. With the light collection difference between the pixels, since it appears as the signal output difference, it may become the factor of generating a noise due to the output irregularity. Moreover, by the oblique light beam, a signal output difference may be generated between the pixel central part of each pixel area and the peripheral part thereof so as to lower the signal output of the peripheral part compared with the pixel central part. Such a signal output difference causes shading on the output screen of an image.
For the above-mentioned problems, JP-A No. 2005-150492 discloses a solid-state image sensor having the interface between an interlayer insulating layer and a protection layer provided with an inclination according to the displacement amount of the plane position between the light receiving sensor part and the micro lens. Although the image sensor improves the light collection efficiency utilizing the refractive index difference between the interlayer insulating layer and the protection layer, since a process of cutting the interlayer insulating layer is provided additionally, a problem of the process complication is involved.
In view of the above-mentioned problems, a solid-state image sensor capable of solving the problems of such as the noise generation or shading by avoiding generation of such as the light collection difference between the pixels or signal output difference even when the central position of the micro lens and the central position of the light receiving element do not coincide with each other in the plan view; and a method for producing a solid-state image sensor, capable of obtaining such a solid-state image sensor by a simple method, are desired.